The present invention relates to a system for optimizing gas turbine performance by minimizing performance loss resulting from cooling and sealing air provided by compressor casing bleed ports.
The axial location or stage at which air is bled from the compressor is determined by the pressure required to drive the specific systems to be serviced by that air. To ensure sufficiently high delivery pressure, in general it is desirable to select a source with the highest possible pressure. However, bleeding air from the earliest possible stage of the compressor will increase overall gas turbine efficiency by reducing the amount of compressor work invested in the extracted air and will therefore reduce the temperature of the extracted air. Therefore, it is desirable to achieve the highest possible system supply pressure from the earliest and lowest pressure stage of the compressor.
Conventionally, compressor belts have been located in various positions in the compressor casing to extract air of proper pressure for turbine cooling and leakage over all turbine-operating conditions. However, minimum supply to sink pressures always occur at conditions other than full load ISO day and, thus, there is excess supply pressure and flow during full load ISO day operations. Consequently, during full load ISO day operation the bleed air must be dissipated across a valve and/or orifice so that the final delivery pressure and flow are as required. The negative consequence of such a system is that the pressure dissipation required is a performance loss, because the work/power used to compress that air is dissipated in the form of total pressure drop.
With reference to FIG. 1, there is shown therein a gas turbine with conventional compressor extraction circuits 10 of the type generally described above. As illustrated, at least a lower pressure extraction circuit 12 and a mid pressure extraction circuit 20 are typically provided. In this exemplary system, the lower pressure extraction line 14 includes a control valve 16 for flow control and an orifice 18 for pressure dissipation. The mid pressure extraction line 22 similarly includes a control valve 24 and an orifice 26.
The invention is embodied in a methodology and corresponding gas turbine cooling and sealing air supply system design for an industrial gas turbine which effectively removes the need to dissipate bleed pressure across an orifice or similar device, thereby to optimize full load ISO performance. Such a system design is realized by providing cross over valves/ejectors which allow mixing of extractions to adjust extraction flow(s) for optimum machine and site condition performance.
Thus, the invention is embodied in a system for bleeding air from plural ports in a multi-stage compressor to provide cooling and/or sealing air to an associated turbine for optimizing gas turbine performance, comprising a first extraction flow path for conducting bleed air from a lower pressure stage of the compressor to the turbine; a second extraction flow path for conducting bleed air from a mid pressure stage of the compressor to the turbine; and a first cross over flow path interconnecting the first extraction flow path and the second extraction flow path for selective cross over flow therebetween, whereby flow through and between the first and second extraction flow paths can be selectively controlled to supply air to the turbine at a proper pressure with an economic mixture of bleed air.
The invention is also embodied in a method for bleeding air from plural ports in a multi-stage compressor to provide cooling and/or sealing air to an associated turbine for optimizing gas turbine performance, comprising: selectively extracting bleed air from a lower pressure stage of the compressor and flowing the low pressure extraction through a first extraction flow path from the lower pressure stage of the compressor toward a first target portion of the turbine; selectively extracting mid pressure bleed air from a mid pressure stage of compressor and selectively flowing the mid pressure bleed air along a second extraction flow path from the mid pressure stage of the compressor toward a second target portion of the turbine; and selectively communicating the first extraction flow path and the second extraction flow path through a first cross over flow path so as to selectively mix air flowing through the first and second extraction flow paths to control pressure of air supplied to at least one of the target portions of the turbine.